Explanatory note:The images (and movies) on the right are
so-called "running difference" images, showing the difference in
brightness from one observation to another. This brings out more
contrast, highlighting the coronal mass ejections, but also introduces
some artifacts. Most notably, most of the dark areas are not really
"dark", they have just dimmed since the last image (or a bright spot
may have moved from one place to another).

Caption:
At 21:30 UT on 17 February the ESA-NASA SOHO spacecraft spotted a
large puff of gas from the Sun. Subsequent images from the LASCO
coronagraph on SOHO confirmed that this coronal mass ejection is
heading towards the Earth. The gas will reach the Earth's vicinity on
Saturday or Sunday, 19 or 20 February. When it hits the Earth's
magnetic shield, it is likely to cause a magnetic storm. It may
provoke spectacular displays of auroras high in the air over sub-polar
regions of the Earth, and perhaps even at lower latitudes in
Scandinavia and North America.

In a second event, at about 10:00 UT on 18 February SOHO and other
spacecraft registered a burst of energetic particles --- solar protons
-- coming from an eruption on the Sun. They may be associated with a
second large mass ejection seen by LASCO, which is not heading for the
Earth.

The proton shower is detected by the EIT instrument as increased noise
due to particle hits on their detector. The plot below shows the
increase in the noise levels caused by this event (click on image
for a larger version).

Satellite controllers will be on the alert this weekend for harmful
effects that the earthward-bound mass ejection may have on their
spacecraft. Users of telecommunications and navigation satellites
may be affected too, as may operators of ground systems that are
vulnerable to the effects of solar storms, such as power transmission
lines.

Most mass ejections from the Sun miss the Earth, or are minor
events. When a large mass ejection is heading towards the Earth it
appears as an expanding bright halo around the Sun, in
SOHO/LASCO images. A mass ejection heading directly away from
the Earth, on the far side of the Sun, has a similar appearance. But in
this case the EIT telescope on SOHO saw shock waves in the solar
atmosphere associated with the mass ejection, making it certainly an
Earth-approaching event.

Half an hour or so before the mass ejection reaches the Earth, it will
wash over SOHO itself, and the CELIAS solar-wind instrument on
the spacecraft will gauge the density of the gas. Only then will
scientists and engineers know how hard the Earth?s space
environment will be hit.